1. Field of the Invention
The present invention relates to a thin-film magnetic head that utilizes a magnetoresistive element for reading the magnetic field intensity of a magnetic recording medium, for example, as a signal, and to a method of manufacturing such a thin-film magnetic head.
2. Description of the Related Art
Performance improvements in thin-film magnetic heads have been sought as recording density of hard disk drives has increased. Such thin-film magnetic heads include composite thin-film magnetic heads that have been widely used. A composite head is made of a layered structure including a write (recording) head having an induction-type electromagnetic transducer for writing and a read (reproducing) head having a magnetoresistive (MR) element for reading that detects a magnetic field through the use of the magnetoresistive effect.
Read heads that exhibit high sensitivity and produce high outputs have been required. In response to such demands, attention has been focused on tunnel magnetoresistive elements (that may be hereinafter called TMR elements) that detect a magnetic field through the use of the tunnel magnetoresistive effect.
The TMR element has a structure in which a lower magnetic layer, a tunnel barrier layer and an upper magnetic layer are stacked on a substrate. Each of the lower magnetic layer and the upper magnetic layer includes a ferromagnetic substance. In general, the magnetic layer closer to the substrate is called the lower magnetic layer and the magnetic layer farther from the substrate is called the upper magnetic layer. Therefore, the terms xe2x80x98upperxe2x80x99 and xe2x80x98lowerxe2x80x99 of the upper and lower magnetic layers do not always correspond to the position in the arrangement of an actual TMR element.
The tunnel barrier layer is a layer made of a thin nonmagnetic insulating film through which electrons are capable of passing while maintaining spins thereof by means of the tunnel effect, that is, through which a tunnel current is allowed to pass. The tunnel magnetoresistive effect is a phenomenon that, when a current is fed to a pair of magnetic layers sandwiching the tunnel barrier layer, a tunnel current passing through the tunnel barrier layer changes, depending on the relative angle between magnetizations of the two magnetic layers. If the relative angle between magnetizations of the magnetic layers is small, the tunneling rate is high. As a result, the resistance to the current passing across the magnetic layers is reduced. If the relative angle between magnetizations of the magnetic layers is large, the tunneling rate is low. The resistance to the current passing across the magnetic layers is therefore increased.
With regard to the structure of a thin-film magnetic head incorporating a TMR element, if the tunnel barrier layer made up of a thin insulating layer is exposed from the medium facing surface that faces toward a recording medium, a short circuit may occur between the two magnetic layers opposed to each other with the tunnel barrier layer in between, during or after lapping of the medium facing surface. Such a structure is therefore not preferred.
To cope with such a problem, the inventors including the inventors of the present application disclose a thin-film magnetic head in U.S. patent application Ser. No. 09/517,580. This head has a structure in which a TMR element retreats from the medium facing surface, and a soft magnetic layer is provided for introducing a signal magnetic flux to the TMR element. The soft magnetic layer extends from the medium facing surface to the point in which the TMR element is located. In the present application this soft magnetic layer is called a front flux guide (FFG) and the thin-film magnetic head having the above-described structure is called an FFG-type TMR head. It is impossible that the TMR element incorporated in the FFG-type TMR head is lapped when the distance between the medium facing surface and the TMR element is controlled by lapping the medium facing surface. Therefore, the FFG-type TMR head has a feature that the medium facing surface of the head is defined by mechanical lapping without creating a short circuit between the two magnetic layers.
Reference is now made to FIG. 18 to FIG. 23 to describe an example of method of manufacturing the FFG-type TMR head. FIG. 18 to FIG. 23 are cross sections that illustrate steps of the method.
In this method, as shown in FIG. 18, a lower electrode layer 102 is formed on a substrate 101. Next, a lower magnetic layer 103, a tunnel barrier layer 104 and an upper magnetic layer 105 are stacked on the lower electrode layer 102 one by one. Next, a resist mask 106 used for patterning the TMR element is formed by photolithography on the upper magnetic layer 105.
Next, the upper magnetic layer 105, the tunnel barrier layer 104 and the lower magnetic layer 103 are selectively etched through ion milling, for example, using the resist mask 106. The TMR element 120 made up of the lower magnetic layer 103, the tunnel barrier layer 104 and the upper magnetic layer 105 that are patterned is thus formed, as shown in FIG. 19. Next, an insulating layer 107 is formed around the TMR element 120 through liftoff. That is, the insulating layer 107 is formed over the entire surface while the resist mask 106 is left. The resist mask 106 is then removed.
Next, as shown in FIG. 20, an FFG layer 109 made of a soft magnetic material is formed on the upper magnetic layer 105 and the insulating layer 107. Next, a resist mask 110 used for patterning the FFG layer 109 is formed by photolithography on the FFG layer 109.
Next, as shown in FIG. 21, the FFG layer 109 is selectively etched through ion milling, for example, using the resist mask 110. The FFG layer 109 is thereby patterned. The FFG layer 109 patterned is T-shaped and has a portion extending from the portion above the upper magnetic layer 105 toward the medium facing surface, and two portions extending from the portion above the upper magnetic layer 105 toward both sides in the direction parallel to the medium facing surface. The resist mask 110 is then removed.
Next, as shown in FIG. 22, hard magnetic layers 111 for applying a bias magnetic field to the TMR element 120 are formed on outer sides of the two portions of the FFG layer 109 extending toward both sides in the direction parallel to the medium facing surface.
Next, as shown in FIG. 23, an upper electrode layer 112 is formed on the FFG layer 109 and the hard magnetic layer 111. Through the foregoing steps, the TMR element 120 of the FFG-type TMR head and its periphery are formed.
Next, the medium facing surface of the head is defined by lapping. Through this lapping the FFG layer 109 is exposed from the medium facing surface and the distance from the medium facing surface to the TMR element 120 is controlled.
The FFG as described above is not limited to a TMR head but may be applied to an MR head having a structure that is disclosed in Published Unexamined Japanese Patent Application Heisei 5-275769 (1993), that is, a structure in which a sense current used for signal detection is fed to the MR element in the direction perpendicular to the film surface of the MR element. Such a structure is called a current perpendicular to plane (CPP) structure in the present application. The structure of the TMR head is included in the CPP structure.
One type of CPP-structure MR head incorporates a multilayer magnetic film made up of a plurality of magnetic layers stacked with nonmagnetic layers in between, in place of the lower magnetic layer 103, the tunnel barrier layer 104 and the upper magnetic layer 105 of FIG. 23. This multilayer magnetic film has a property that the RKKY interaction occurs between the magnetic layers and the directions of magnetization of the magnetic layers are thereby made antiparallel when the material and the thickness of the nonmagnetic layers are suitably chosen. The multilayer magnetic film thus exhibits the giant magnetoresistive (GMR) effect. Such a multilayer magnetic film is disclosed in Published Unexamined Japanese Patent Application Heisei 4-360009 (1992), Published Unexamined Japanese Patent Application Heisei 9-129445 (1997) and Published Unexamined Japanese Patent Application Heisei 5-90026 (1993), for example. The multilayer magnetic film is called an antiferromagnetic coupling-type multilayer magnetic film in the present application. The CPP-structure GMR head incorporating an antiferromagnetic coupling-type multilayer magnetic film, such as the one disclosed in Published Unexamined Japanese Patent Application Heisei 5-275769, is called a CPP-structure GMR head in the present application.
In place of the antiferromagnetic coupling-type multilayer magnetic film mentioned above, it is possible to utilize a spin-valve-type multilayer magnetic film that is disclosed in U.S. Pat. No. 5,159,513. The spin-valve-type multilayer magnetic film may be a dual-spin-valve-type multilayer magnetic film that is disclosed in Published Unexamined Japanese Patent Application Heisei 10-91921 (1998).
When an areal recording density greater than 100 gigabits per square inch is implemented, even a head incorporating a TMR element is not capable of producing a sufficient output and a sufficient signal-to-noise (S/N) ratio. The CPP-structure GMR head as mentioned above is therefore required.
According to the method of manufacturing the FFG-type TMR head illustrated in FIG. 18 to FIG. 23, the FFG layer 109 is required to be formed on the integrated surface of the TMR element. In this case, as shown in FIG. 20, the top surface of the upper magnetic layer 105 of the TMR element occupies an only small portion of the surface on which the FFG layer 109 is formed while the greater part of this surface is the top surface of the insulating layer 107. Therefore, the FFG layer 109 is almost directly formed on the insulating layer 107.
However, when the FFG layer 109 is directly formed on the insulating layer 107, the soft magnetic property of the FFG layer 109 is reduced. As a result, a problem that a read output of the head to be obtained is insufficient thereby results. The reason is considered to be a bad orientation of the FFG layer 109 directly formed on the insulating layer 107.
In Published Unexamined Japanese Patent Application Heisei 8-153310 (1996), a technique is disclosed for making a flux guide layer on a base layer of Ta or Cr, for example, that is formed on the magnetic layer having the magnetoresistive effect. It is thus possible that the FFG layer 109 is formed on a base layer that is formed on the upper magnetic layer 105 and the insulating layer 107 in the FFG-type TMR head, too.
However, if the FFG layer 109 is formed on a base layer made of a nonmagnetic material such as Ta or Cr that is formed on the upper magnetic layer 105, the following problem results. It is required that the upper magnetic layer 105 is magnetically coupled to the FFG layer 109, so that the magnetic flux that enters from the FFG layer 109 during operation is efficiently brought to the upper magnetic layer 105. However, it is impossible that the upper magnetic layer 105 is magnetically coupled to the FFG layer 109 if the FFG layer 109 is formed on the base layer made of a nonmagnetic material that is formed on the upper magnetic layer 105. It is therefore impossible that the FFG layer 109 fully exhibits its function.
The foregoing problem similarly applies to the case in which the FFG layer is provided in a CPP-structure GMR head.
It is an object of the invention to provide a thin-film magnetic head comprising a magnetoresistive element and a soft magnetic layer that introduces a signal flux to the magnetoresistive element, and a method of manufacturing such a thin-film magnetic head for improving the soft magnetic property of the soft magnetic layer and improving the output of the head.
A thin-film magnetic head of the invention comprises: a magnetoresistive element having two surfaces that face toward opposite directions and a side portion that connects the two surfaces to each other; a first electrode layer and a second electrode layer each of which is directly or indirectly connected to each of the surfaces of the magnetoresistive element and provided for feeding a current used for signal detection to the magnetoresistive element; an insulating layer provided between the first and second electrode layers and located adjacent to the side portion of the magnetoresistive element; a soft magnetic layer introducing a signal magnetic flux to the magnetoresistive element, the soft magnetic layer touching one of the surfaces of the magnetoresistive element and extending from a region in which the magnetoresistive element is located to a region in which the insulating layer is located; and a base film located between the soft magnetic layer and the insulating layer and used as a base when the soft magnetic layer is formed.
A method of the invention is provided for manufacturing a thin-film magnetic head comprising: a magnetoresistive element having two surfaces that face toward opposite directions and a side portion that connects the two surfaces to each other; a first electrode layer and a second electrode layer each of which is directly or indirectly connected to each of the surfaces of the magnetoresistive element and provided for feeding a current used for signal detection to the magnetoresistive element; an insulating layer provided between the first and second electrode layers and located adjacent to the side portion of the magnetoresistive element; and a soft magnetic layer introducing a signal magnetic flux to the magnetoresistive element, the soft magnetic layer touching one of the surfaces of the magnetoresistive element and extending from a region in which the magnetoresistive element is located to a region in which the insulating layer is located. The method includes the steps of: forming the first electrode layer; forming the magnetoresistive element and the insulating layer on the first electrode layer; forming a base film on the insulating layer, the base film being used as a base when the soft magnetic layer is formed; forming the soft magnetic layer on the base film and the magnetoresistive element; and forming the second electrode layer on the soft magnetic layer.
According to the thin-film magnetic head or the method of manufacturing the same of the invention, the soft magnetic layer is formed on the base film that is formed on the insulating layer while the base film is not located between the magnetoresistive element and the soft magnetic layer.
According to the thin-film magnetic head or the method of the invention, the base film may be made of a nonmagnetic metal material. In this case, the nonmagnetic metal material may include Cr or NiCr.
According to the thin-film magnetic head or the method of the invention, the magnetoresistive element may incorporate a tunnel barrier layer and two magnetic layers opposed to each other, the tunnel barrier layer being located between the magnetic layers.
According to the thin-film magnetic head or the method of the invention, the magnetoresistive element may incorporate an antiferromagnetic coupling-type multilayer magnetic film.
According to the thin-film magnetic head or the method of the invention, the magnetoresistive element may incorporate a spin-valve-type multilayer magnetic film. The spin-valve-type multilayer magnetic film may be a dual-spin-valve-type multilayer magnetic film.
According to the thin-film magnetic head or the method of the invention, the soft magnetic layer may be made up of a plurality of layers.
Other and further objects, features and advantages of the invention will appear more fully from the following description.